Climate changes significantly influence the planet geosphere. One of the major impacts on climate changes is the emission of various greenhouse gases to the atmosphere which amplify global warming. Most of the greenhouse gases emitted originate from human activity, mainly as a by-product of the burning of fossil fuels (e.g., coal, oil, gasoline, natural gas) with the major gas emitted being CO2. Reduction of CO2 emissions is necessary, until alternative energy sources are available, or until other inexpensive, clean, and plentiful technologies are available.
Fossil fuels appear to be the dominant energy source for this century, as no alternative energy supply is poised to significantly replace fossil fuel energy without other limitations. Moreover, global energy consumption is increasing significantly, concomitant with an increase in global standards of living, in many parts of the world. Developing an effective method for decreasing or stabilizing atmospheric CO2 concentrations is critical in order to prevent, or at least mitigate massive global climate changes; improving the efficiency of energy production and utilization, and developing renewable energy sources, cannot fully address the problems caused by current (and future) greenhouse gas emissions.
An increase in atmospheric CO2 will affect the planet's hydrosphere. In water, CO2 is in a chemical equilibrium with bicarbonate (HCO3−) and carbonic acid (H2CO3) (equation 1). Changing the concentration of one of the components of this equilibrium will accordingly change the pH.H2O+CO2 (g)CO2 (Aq)H++HCO3−2H++CO32−H2CO3  (1)
The pH and the CO2 concentration also affect chemical processes in water and formation of minerals. For instance, when basic conditions prevail, equilibrium considerations favor precipitation of the bicarbonates and carbonic acid groups as carbonate minerals. On the other hand, acidic conditions release CO2 by dissolution and dissociation of the carbonates.
It is clear that reduction of CO2 emissions is necessary to avoid potentially harmful changes to the biosphere. CO2 sequestering is a known method for reducing CO2 emissions to the atmosphere. For example the Sleipner oil and gas field, located in the North Sea, is used to store compressed CO2 which was pumped into a 200-meter-thick sandstone layer, about 1000 meters below the seabed. Approximately 1 million metric tons of CO2 (equivalent to about 3% of Norway's total annual CO2 emissions) have been sequestered annually at Sleipner.
The long-term efficiency of such sequestering remains a subject of intense study and debate. In particular, uncertainties in storage lifetimes (due to leakage), seismic instability, changes in layered structures due to pressure and/or chemical reactions with and/or initiated and/or catalyzed by the stored CO2 and potential migration of buoyant CO2, raise serious doubts as to the long-term integrity of such systems.
Mineral sequestering involves the reaction of CO2 to form geologically stable carbonates, i.e. mineral carbonation. There have been several methods suggested to achieve carbonation, based largely on acid-base reactions between CO2 and various kinds of silicates. An underground injection scheme, carried out at 105° C. and a pressure of 90 atm, CO2 was used to test the validity of mineral-trapping of CO2. This injection scheme failed due to sluggish kinetics of the reaction. It is believed, however, that injected CO2 into aquifer material, and interaction over geological time scales, may achieve the desired result.
CO2 trapping and storage is a difficult task and there are many remaining challenges. Mineral carbonation is a promising method as a number of advantages of reducing the concentration of CO2 by mineral carbonation exist. One advantage is long-term stability of the formed carbonates, which are environmentally safe and stable materials over geological time frames. Another advantage is the vast availability of raw materials to sequester CO2. Another advantage of mineral carbonation is its potential to be economically viable, since the overall process is exothermic. In addition, its potential to produce value-added by-products during the carbonation process may further compensate its costs. Another advantage of mineral carbonation process is also the large availability of sites at which sequestering can be practiced.
Thus, feasible means of CO2 sequestering in order to sufficiently reduce the CO2 concentration in the atmosphere and in water on a practically useful time-scale is currently lacking.